The present invention relates to supplying a compensating leading or lagging reactive type current to an A.C. electrical power system for stabilization of voltages, and more particularly, to a regulating system having an RMS composite controller system for the development of the compensating reactive current.
It is known that electric power systems which supply highly erratic reactive loads, e.g., electric arc furnaces, are typically characterized by poor voltage regulation. Locations on utility systems remote from the generation of the power also are typically characterized by poor voltage regulation. Compensating and regulating systems, herein simply referred to as regulating systems, which alleviate this condition are disclosed in several of my issued U.S. Patents including U.S. Pat. Nos. 4,143,315; 3,936,726; 3,926,727; and 4,121,150, all assigned to the assignee of the present invention. A further regulating system is described in my U.S. Patent Application Ser. No. 242,784, filed Mar. 11, 1981 and also assigned to the assignee of the present invention. The foregoing U.S. Patents and the Application are herein incorporated by reference into the present application.
U.S. Pat. No. 4,143,315 and U.S. Application Ser. No. 242,784 describe regulating systems for a three phase power system that exert individual control of each of the phase-to-phase voltages. By employing a common reference, the system voltages are regulated to be of equal value. Thus, the negative sequence component of voltage is regulated and the positive sequence component of voltage is also regulated to the desired value. The required rating of the reactive converter is the sum of the ratings required to regulate the negative sequence component and to regulate the positive sequence component for the disturbances or conditions encountered. The rating of the reactive converter is commonly termed "MVAR". The MVAR represents the magnitude of the rating and corresponds to the magnitude of available compensating reactive current typically derived from thyristor switched inductor circuits.
In some applications such as with utility power systems the negative sequence component is limited and is considered tolerable. In such cases the MVAR rating and therefore the cost of the reactive converter is reduced if it is supplied to only regulate the positive sequence component. To employ the regulating systems described by U.S. Pat. No. 4,143,315 or by U.S. Application Ser. No. 242,784 would consume reactive converter rating for the correction of the negative sequence component if such correction occurred and thus would decrease the rating available for correction of positive sequence disturbances. Thus, for these cases it is desired to regulate the positive sequence component only.
Accordingly, it is an object of this invention to provide a regulating system for supplying a leading or lagging reactive type current to a three phase power system to compensate for positive sequence disturbances.
Another object of this invention is to provide an accurate regulating system for accurately compensating for positive sequence disturbances.
A further object of the present invention, is to provide RMS composite control signals derived from the three phase quantities of the power system as means for correspondingly improving voltage regulation necessitated by power disturbances.
These and other objects of the present invention will become apparent to those skilled in the art upon consideration of the following description of the invention.